vent (n.)

c. 1400, "anus," from Old French vent from verb eventer (see vent (v.)) and in part from Middle English aventer, from the French verb. Perhaps also merged with or influenced by Middle English fent "opening or slit in a the front of a garment (usually held closed with a brooch)," c. 1400, from Old French fente, from Latin findere "to split" (from PIE root *bheid- "to split"). Meaning "outlet for water," also "air hole, breathing hole" is from mid-15c. Meaning "action of venting" is recorded from c. 1500.